M2 Transport across the Membrane Flashcards
What are the 5 main things membranes consist of?
- Phospholipids
- Proteins
- Cholesterol
- Glycolipids
- Glycoproteins
Describe the function of phospholipids in cell membranes.
- Form a bilayer.
- Allow transport of lipid soluble substances and very small molecules through the membrane.
- Do not allow transport of water soluble (polar) substances and ions through the membrane.
- Give membrane flexibility.
What are the 2 different types of proteins in cell membranes.
Extrinsic (on the surface)
Intrinsic (span the bilayer from one side to another)
- carrier proteins and channel proteins
What are the roles of proteins in cell membranes?
- Provide structural support
- Form cell surface receptors for cell recognition
- Adhesion of cells
- Receptor sites e.g. for hormones
What is the role of cholesterol in cell membranes?
- reduces lateral movement, providing strength and stability.
- reduces fluidity at high temperatures.
- prevents leakage of water and dissolved ions from the cell.
What are the roles of glycolipids and glycoproteins?
- act as recognition sites
- maintain stability of membrane
- help cells attach to form tissues
- glycoproteins specifically form receptors for hormones and neurotransmitters
What is diffusion? DEFINITION
The net movement of a substance down a concentration gradient.
Describe the two proteins involved in facilitated diffusion.
Protein channels:
- Hydrophilic channel through the phospholipid bilayer.
- Permanently open
Carrier proteins:
- Molecule binds to proteins, protein changes shape and molecule is released inside of the cell.
What are the factors that affect the rate of Diffusion across cell membranes?
- Surface Area
- Differences in Conc Gradient
- Number of Channel/carrier proteins
What is osmosis? DEFINITION
The net movement of water molecules from an area of high water potential to an area of lower water potential through a partially permeable membrane down a water potential gradient.
What is water potential?
Pressure caused by water molecules moving around and colliding with the cell membrane.
What has the highest water potential? How do you measure it?
Pure water = 0kPA
the more negative the number the lower the water potential.
What is solute potential?
The amount the water potential of a solution is lowered by when solutes restrict the movement of water molecules (due to hydration shells).
What is pressure potential?
The positive contribution made by pressure to water potential (e.g. plant cell walls), increasing water potential.
What is the equation for water potential in plant cells?
Water Potential = Solute Potential + Pressure Potential
What kind of water potential do hypertonic, isotonic and hypotonic solutions have?
Hypertonic: Higher water potential in the cell than in the solution (cell is plasmolysed)
Isotonic: The same water potential
Hypotonic: Lower water potential in cell than in solution (cell is turgid/bursts)
What is incipient plasmolysis?
When the membrane pulls away from the cell wall so it is no longer pressing on it (the pressure potential of the cell drops to 0).
What happens in a plant cell when it is turgid?
The membrane is pressing against the cell wall.
How do you know under a microscope if a solution is isotonic?
50% of the cells are plasmolysed.
What is the definition of active transport?
The movement of molecules/ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins.
Describe the process of active transport.
1) Molecule/ion binds to a receptor site on one side of the carrier protein.
2) On the inside of the cell, ATP binds to the carrier protein, which acts as an enzyme (ATP -> ADP + Pi)
3) This causes the carrier protein to change shape. The Pi is still bound to it at this stage.
4) The molecule/ion is released to the other side of the membrane.
5) The phosphate group is released and the carrier protein returns to its original shape.
Carrier proteins are highly ____, so __________ binding occurs.
Specific
Complementary
Describe the process of co-transport in the ileum.
1) Na+ are actively transported out of the cell into the bloodstream - low Na+ conc in the cell.
2) Na+ diffuse into the cell, down the conc gradient through a co-transport protein taking glucose with it - high glucose conc in the cell.
3) Glucose leaves cell by facilitated diffusion and enters the bloodstream.
Other than glucose, what is also co-transported with Na+?
Amino Acids
How do you determine the solute potential of a plant cell?
Place plant tissues in different concentrations of salt or sugars. Observe using a microscope the concentration in which 50% of cells are plasmolysed (isotonic).
